In imaging systems commonly used today, a charge retentive surface is typically charged to a uniform potential and thereafter exposed to a light source to thereby selectively discharge the charge retentive surface to form a latent electrostatic image thereon. The image may comprise either the discharged portions or the charged portions of the charge retentive surface. The light source may comprise any well known device such as a light lens scanning system or a laser beam. Subsequently, the electrostatic latent image on the charge retentive surface is rendered visible by developing the image with developer powder referred to in the art as toner. The most common development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the charge retentive surface to form a powder image thereon. This toner image may be subsequently transferred to a support surface such as plain paper to which it may be permanently affixed by heating or by the application of pressure or a combination of both.
In order to fix or fuse the toner material onto a support member or substrate permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the substrate or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the substrate.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the substrate to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. Typical of such fusing devices are two roll systems wherein the fusing roll is coated with a compliant material, such as a silicone rubber or other low surface energy elastomer or, for example, tetrafluoroethylene resin sold by E. I. DuPont De Nemours under the trademark Teflon. In these fusing systems, however, since the toner image is tackified by heat it frequently happens that a part of the image carried on the supporting substrate will be retrained by the heated fuser roller and not penetrate into the substrate surface. The tackified toner may stick to the surface of the fuser roll and offset to a subsequent sheet of support substrate or offset to the pressure roll when there is no sheet passing through a fuser nip resulting in contamination of the pressure roll with subsequent offset of toner from the pressure roll to the image substrate.
To obviate the foregoing toner offset problem it has been common practice to utilize toner release agents such as silicone oil, in particular, polydimethyl silicone oil, which is applied to the fuser roll surface to a thickness of the order of about 1 micron to act as a toner release material. These materials possess a relatively low surface energy and have been found to be materials that are suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner image carried on the support material Thus, a low surface energy, easily parted layer is presented to the totters that pass through the fuser nip and thereby prevents toner from adhering to the fuser roll surface.
Various systems have been used to deliver release agent fluid to the fuser roll including the use of oil soaked rolls and wicks with and without supply sumps as well as oil impregnated webs. It has be seen in various systems in which a uniform amount of release fluid can be applied to the surface of the fuser roll. When the copy substrate dimension normal to the direction of travel of the substrate is less than the total length of the fuser roll end of the roll beyond the copy paper (i.e. the portion of the roll surface not in contacted by the copy paper) continuously take on oil without removal thereof while the area contacted by the copy paper has some of the oil removed by the copy paper as it moves through the nip between the fuser roll and pressure roll structures. The foregoing results in the swelling of the ends of the rolls to such a degree that the fuser roll and/or pressure roll coating weakens and blowout occurs resulting in paper handling problems and fuser roll and/or pressure roll failure.
The following references may be of relevance to the present invention:
U.S. Pat. No. 3,941,558 PA1 Patentee: Takiguchi PA1 Issued: Mar. 2, 1976 PA1 U.S. Pat. No. 4,258,648 PA1 Patentee: Leising et al. PA1 Issued: Mar. 31, 1981 PA1 U.S. Pat. No. 4,393,804 PA1 Patentee: Nygard et al PA1 Issued: Jul. 19, 1983 PA1 U.S. Pat. No. 4,557,588 PA1 Patentee: Tomosada PA1 Issued Dec. 10, 1985 PA1 U.S. Pat. No. 4,939,552 PA1 Patentee: Nakanishi PA1 Issued: Jul. 3, 1990 PA1 U.S. Pat. No. 5,045,890 PA1 Patentee: DeBolt et al. PA1 Issued: Sep. 3, 1991 PA1 U.S. Pat. No. 5,049,944 PA1 Issued: Sep. 17, 1991 PA1 JPPN-58-184173 (A) PA1 Patentee: Katou PA1 Published: Oct. 27, 1983 PA1 JPPN-61-251881 (A) PA1 Patentee: Takizawa PA1 Published: Nov. 8, 1986
Patentee: DeBolt et al.
The foregoing references may be summarized as follows:
U.S. Pat. No. 3,941,558 discloses a rolled web impregnated with silicone oil for preventing offset. The web has a thickness of two mm, a total length of 50 cm, and travels one cm per thousand copies between the supply and take-up rollers. This system transfers about 0.003 cc of oil to the fuser per copy.
U.S. Pat. No. 4,258,648 discloses a heat and pressure roll fusing apparatus for fixing toner images to copy substrates. The apparatus has a tapered doner roll applicator for the fuser roll.
U.S. Pat. No. 4,393,804 discloses a rolled web system that moves between a supply core and take-up roller. A felt applicator supplies oil from a supply reservoir to the web. The take-up core is driven by a slip clutch at a speed greater than the speed of the pressure roller, thus exerting tension on the web. The web is between one and two mm in thickness and moves at a constant speed of 5 cm per 200 to 1,000 copies.
U.S. Pat. No. 4,557,588 discloses an image forming apparatus such as an electrophotographic copier, microfilm equipment, recording equipment, facsimile or printer. A movable cleaning member is maintained in contact with a member to clean its surface and the movement of the cleaning member is variably controlled according to the state of the image formation.
U.S. Pat. No. 4,939,552 discloses a cleaning device for cleaning the surface of an element of a copying apparatus to be cleaned by contacting a cleaning web therewith is connected to a driving mechanism of a scanning member of the coping apparatus and is driven in correlative movement with the scanning member. It is driven only when the scanning member returns to its original position by a one way clutch and by a constant amount of movement irrespective of the amount of movement of the scanning member.
U.S. Pat. No. 5,045,890 discloses a fuser apparatus for applying offset preventing liquid to a fuser roll including :a supply core; a rotatable take-up core; an oil impregnated web member adapted to be moved from the supply core to the take up core; a motor mechanically coupled to the take up roll for driving the web member from the the supply core to the take up core; a pressure roll in engagement with the web member and positioned to provide a contact nip for the web member with the fuser roll opposite the pressure roll wherein the contact of the web member with the fuser roll transfers oil from the web member to the fuser roll, and a controller to vary the duty cycle operation of the motor to drive the web member at a relatively constant linear speed at the contact nip, the controller including a timer to monitor the cumulative time of operation of the motor to progressively decrease the duty cycle of the motor in response to the cumulative time of operation wherein the progressively decreased duty cycle of operation compensates for the increasing radius of the web member on the take up roll to maintain the relatively constant linear speed at the contact nip.
U.S. Pat. No. 5,049,944 discloses apparatus for applying offset preventing liquid to a fuser roll including an oil impregnated web to be moved relative to a fuser roll. A timer is employed to monitor the cumulative time of operation of a motor used to drive the web relative to the fuser roll and to progressively decrease the cycle of the motor so that essentially a uniform amount of the web is moved at each cycle.
JPPN-58-184173 (A) discloses a fuser apparatus in which one of the rolls is crowned in the center and the other is flared toward one end. The flared roller is also mounted at an angle to the center line of the crowned roller.
JPPN-61-251881 (A) discloses a fixed roller having an inverted crow shape along its length, which engages a belt entrained about two crown shaped rollers to act a part of a fixing device.
Additionally, there are several automatic printing machines commercially available, such as the Xerox 5028 model copier, which employ webs for providing release agents to fuser rolls. Other examples of such commercial devices, presently or currently available, include the Canon model 3225, 3725, 3000 series, 4000 series and 5000 series products. These products also all have liquid release agent impregnated webs supported between a supply roll and a take-up roll and urged into contact with the fuser roll by an open celled foam pinch roll.
In accordance with one aspect of the present invention there is provided an apparatus for applying offset preventing liquid to a fuser roll, comprising a web material having offset preventing liquid in pregnated therein and an elongated pinch roll. The elongated pinch roll has an outer surface mounted in engagement with the web material to urge the web material into contact with the fuser roll to apply the offset preventing liquid to the fuser roll. The pinch roll applies a first pressure over a first region and a second pressure over a second region in the web so that the web applies a greater amount of offset preventing liquid to the fuser roll over the first region than over the second region.
Pursuant to another aspect of the present invention there is provided an apparatus for fusing toner to print substrate, comprising a fuser roll and a pressure-roll. The fuser roll and the pressure roll form a nip with the fuser roll adapted to receive the substrate. A web material having offset preventing liquid in pregnated therein and an elongated pinch roll is provided. The elongated pinch roll has an outer surface mounted in engagement with the web material to urge the web material into contact with the fuser roll to apply the offset preventing liquid to the fuser roll. The pinch roll applies a first pressure over a first region and a second pressure over a second region in the web so that the web applies a greater amount of offset preventing liquid to the fuser roll over the first region than over the second region.